We hypothesised (i) that sheep grazing a monoculture of tedera (Bituminaria bituminosa (L.) C.H. Stirton var. albomarginata and var. crassiuscula) would not show signs of photosensitisation or ill health, and (ii) that when given free grazing choice they would show a repeatable preference for certain accessions of tedera related to their chemical composition. We tested this by grazing a group of young merino wethers on a monoculture containing seven accessions of tedera for 21 days. General health was assessed via daily visual checks for skin pinkness on the nose and ears, weekly measures of liveweight, condition score, and blood analysis compared with a group of control sheep fed wheaten hay ad libitum. The Chesson–Manly selection index was used to examine the relative preference of sheep for the seven accessions of tedera over the 21 days. Each accession of tedera was sampled weekly to estimate the dry matter on offer, and these samples were also analysed for crude protein, neutral detergent fibre, acid detergent fibre, in vitro digestibility, water soluble carbohydrates, minerals, and concentrations of the furanocoumarins psoralen and angelicin. None of the sheep showed any signs of ill health, with all blood parameters being within the normal reference range. All sheep gained weight and body condition over the 21 days. The difference in the rate of gain in condition score in favour of the sheep grazing tedera over the 21 days (0.014 v. 0.002 unit/sheep.day) was significant (P < 0.001). Sheep showed repeated preference for accessions T31 and T43 (α >0.143). Nutritive value of all accessions of tedera was high. However, only acid detergent fibre and neutral detergent fibre affected the relative preference of the sheep (P < 0.05) and they were only weakly correlated (r2 = 0.208 and 0.165, respectively). We conclude that there are accessions of tedera that are preferred by sheep that could be used to fill the autumn feed gap experienced in the south of Western Australia without any risk to the health of the sheep.
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Vol. 64 • No. 4